Download - Mesoporous materials
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Mesoporous Materials – Synthesis and Applications
Vijaykumar S.Marakatti,PPISR, Bangalore.
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Outline of the talk
Introduction to porous materials
Classification of porous materials
Synthesis mechanism of mesoporous materials
Applications of mesoporous materials
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Introduction“the overwhelming tendency for solids to minimize void space within their structure” is inherent , porous materials are difficult to make naturally.
But Einstein say “ in the middle of difficulty lies opportunity”
The above statement was made true by the Mobil scientist in the year of 1992 by successfully synthesizing the Mesoporous materials (MCM-41 and MCM-48) by using soft template strategy.
This opened a new area of materials called Mesoporous materials, and still lot of work are fascinating in this field.
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What are Porous materials
The history of porous materials began with the zeolites having aluminoisilicates framework which was synthesized by the use single template molecule with small pore.
Most generalized definition of porous materials is continuous and solid network material filled through voids.
A material can be recognized as porous if its internal voids can be filled with gases.
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Classification of porous materials
Depending on pore size Depending on building framework
Micropoorus Mesoporous Macroporous
<2nm 2-50 nm >50nm
Purely inorganic Organic Inorganic hybrid
Purely organic
ZSM-5 MCM-41 Sponge
Silica MOF organic porous polymers
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Mesoporus Materials Meso a Greek prefix – “ in between ” - micro and macro porous system Mesoporous materials may be ordered or disordered.
They possess high Surface area -400 -1000 m2/g Large pore volume High stability -500 -600 °C
They are usually synthesized by the use of Soft template method.
Ex: MCM-41,SBA-15,FDU-11,IITM-56 etc.
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Difference between the zeolites and mesoporous materials
Zeolites Mesoporous MaterialsHighly crystalline Periodic arrangement with amorphous in
nature
TO4 networks TO4,TO5 and TO6 networks
Si and Al are four connected by covalent bond, less surface hydroxyl groupsHydrophobic surface area
Si and Al are 2 or three connected ,more surface hydroxyl groups Hydrophilic surface area
High hydrothermal stability Less hydrothermal stability
Crystalline walls and are thick Amorphous walls and are thin
Synthesis temp is high (80 – 300 °C)Long crystallization time
Synthesis temp is low (-10 to 120°C)Formation rates are fast
Aqueous media is required for crystallization
Non –aqueous solvents and non polar solvents can be used
Synthesis of zeolite is carried out in neutral /weakly acid media
Synthesis pH rang is from 0 to 12
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Synthesis of mesoporous materials
Soft template (endo template)
• Uses soft templates like organic molecules .
•Good shape , Size and morphology. simple• SBA-15 ,MCM-41 etc
Hard template (exo template, nano casting)
• Uses inorganic materials like silica, carbon etc
• Tedious work up, hard to get good morphology and costly
CMK-1
Meso-silica
CMK-1
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Synthesis of mesoporous materials using soft template strategy
1. Surfactants.2. Formation of Micelles.3. Inorganic precursor .4. Interaction of Micelles with inorganic precursor.5. Hydrothermal treatment followed by separation and drying6. Removal of template.7. Proposed mechanism8. Characterization of material.
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1. Surfactant/ Template/Structure directing agent. Large organic molecules(High molecular weight) with both hydrophilic and hydrophobic groups.
Depending upon charge they can be classified as
Cationic Anionic Non ionic/neutral•Excellent solubility•High critical Micelle con.•acidic and basic media• toxic and expensive
•Excellent solubility• repulsion between the anionic surfactant is more.
•Excellent solubility• High critical micelle temp.•Acidic / basic media• non-toxic and cheap
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2. Formation of micelle• At a Low surfactant concentration will favor arrangement on the surface.
• As the concentration increases surface being more crowded as result molecule arrange in to micelles.
• At certain concentration the surface is completely loaded and any further addition leads to the Micelle arrengment.This conc. is known as CMC.
• Beyond the CMC self assembly of micelle occurs to from 3D and 2D rod like arrays.
• Different template have the different CMC.
• To get ordered materials – 0 to20 mg/L
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Different type of surfactant arrangement
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What Makes them to show different type of arrangements ? 1. Critical micelle concentration Low micelle conc. are good to get ordered materials.
2. Packing parameter (g) g = V / ao l
V=Total volume of surfactant hydrophobic chains+ co-solvnet.ao= Effective hydrophilic head group area at the aq. micelle surface.l = kinetic surfactant tail length.
g <1/3 = cubic and 3 D hexagonal,1/3<g>1/2 = 2D hexagonal1/2<g>2/3 = cubicg=1 = Lamellar
3. The hydrophilic and hydrophobic Volume ratio (VH/VL)
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3.Inorganic precursor and pHInorganic Precursor silica depends upon pHBasic synthesis (pH =9.5 to 12.5)-Polymerization and cross Linkage of silicate species are reversibleSilica gel, colloidal sol, Water glass , TEOS etc.Acidic synthesis(pH= 1 to 2 )- Irreversible.- Slow hydrolysis TEOS is preferred.
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4. Interaction of Micelles with inorganic precursor.
Direct interaction of Surfactant with inorganic precursor
Basic -Medium Acidic-Medium
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Interaction of Surfactant with inorganic precursor through intermediate ions
Basic -MediumAcidic-Medium
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Interaction of non ionic Surfactant with inorganic precursor through intermediate ions.
Hydrogen bonds favors most of times
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5. Hydrothermal treatment followed by separation and drying.
Method to improve mesoscopic regularity's of products.
Reorganization, growth and crystallization
80 -150 °C is temperature is usually used.
High temperature will lead to the disorder and decomposition of surfactants.
Separation – filtration or centrifugation.
Washing –alcohol or water. Basic media needs through washing.
Drying at room temperature is good.
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6. Removal of template. Removal of template will give rise to mesoporosity
Different ways by which template can be removed
Calcination•Slow heating rate.• N2 -1 hr O2- 4-6 hr – 2 °C/min• O2-1 °C/min• No surfactant recover• low Surface silanol groups • Not good for low thermal stable materials•P-123 -550 °C• CTAB -350 °C
Solvent Extraction• Solvent ethanol /THF• small HCl is added• Surfactant can be reused
• Microwave•Ultraviolet rays O3 and O
Light irradiation
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p6mmIa3d,
Pm3n
Im3mFd3m
Fm3m.
MCM-48
FDU-2SBA-16
KIT-5
SBA-1 and 6
SBA-15
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Proposed mechanisms for synthesis mesoporous materials
1. Silicate rod assembly
2 or 3 monolayer's of silicates species first deposits on isolated surfactant miceller rods
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2. Cooperative self assembly
Low concentration Surfactant
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3. True liquid crystal templating route
High concentration Surfactant
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Complete synthesis summary
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7. Characterization of mesoporous materials1. Low angel XRD 0.5 -5 -2theta - orederness / disorder.
2. N2 sorption measurements –BJH method
Surface area/pore diameter /pore volume
3. TEM images Order ,Morphohology , Wall thickness
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Applications
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Application Chemical Catalysis1. Mesoporous Materials as catalyst
Al-MCM-41 ,B-MCM-41, Sn-SBA-15 - Acidic K- AlMCM-41 , Cs-AlMCM-41 -basicTiMCM-41 ,V-MCM-41 -Redox
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2.Mesoporous Materials as catalyst support• Noble metal supported catalyst supportsAu-McM-41 , Pt- CMK-3• Metal oxide supported catalysis Fe2O3- MCM-41 ,RuO2-SBA-15• Metal complex supported catalystsMn-Salen –SBA-15
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3. Application in environmental catalysisImmobilization of enzyme on Mesoporous Materials as catalysts Enzymes are excellent biocatalysts with high selectivity and efficiency in environment field, chemical and pharmaceutical industries are limited by their poor stability and chemical sensitivity
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4. Good adsorbents
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5.Applications in Biomedical field
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1) Sustained Drug Release System
M. Vallet-Regi, et al. “A New Property of MCM-41: Drug Delivery System”, Chem. Mater. 2001, 13, 308-311.
Virtually any drug within a size range compatible with the size of the meso-channels has potential to be encapsulated and further deliver intracellularly.
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2. Mesoporous Materials for Bone Tissue Engineering
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Mesoporous Bioactive scaffoldsScaffolds are needed that can act as temporary templates for bone regeneration and actively stimulate vascularized bone growth so that bone grafting is no longer necessary.
Bioactive glass is an ideal material because it rapidly bonds to bone anddegrades over time, releasing soluble silica and calcium ions that are thought to stimulate osteoprogenitor cells.
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1 Day
3 Day
7 Day
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6.Mesoporous Polymers
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Pioneers in Mesoporous Materials
Galen Stucky SBA-15
Ryong RyooKIT -6Hard templateCMK materials
Fudan universityFDU-11
P.SelvumIITM-56, NCCR-56
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Thank you
References:“On the Controllable Soft-Templating Approach to Mesoporous Silicates”Ying Wan and Dongyuan Zhao, chemical reviews, Volume 107, Number 7 .“Soft templating strategies for the synthesis of mesoporous materials: Inorganic,organic–inorganic hybrid and purely organic solids”Nabanita Pal, Asim Bhaumik, Advances in Colloid and Interface Science 189–190 (2013) 21–41